For a variety of reasons, it is often greatly desirable to suspend particles in liquid detergent compositions. For example, because there are certain components (e.g. bleaches, enzymes, perfumes) which readily degrade in the hostile environment of surfactant-containing detergent liquids, these components are often protected in capsule-type particles (see, for example, U.S. Pat. No. 5,281,355) and these capsule-type particles may be suspended in liquid detergent compositions. Other components that may be protected and suspended in this way are, for instance, polyvinylpyrrolidone, aminosilicones, soil release agents and antiredeposition agents. Such particles may vary significantly in size but, usually, their size is in the range of from 300 to 5000 micrometers.
Furthermore, when the liquid detergent composition is translucent or transparent, it may be desirable to suspend coloured particles or capsules of similar size in said liquid composition so as to improve the visual appearance thereof.
Shear thinning gel-type detergent compositions are generally suitable for stably suspending particles therein, since they usually have adequate viscosity when in rest or under very low shear. On the other hand, owing to their shear thinning properties, such gel-type compositions have much lower viscosity when under pouring shear.
One way of formulating such gel-type detergents is by changing a non-gelled formulation so as to form an internal lamellar-phase structure therein which structure gives the desired properties to the thus-formed gel-type detergent.
WO-A-99/27065, WO-A-99/06519 and U.S. Pat. No. 5,820,695 disclose gel-type laundry detergent compositions having an internal structure. These documents teach systems wherein soap or fatty acid in combination with sodium sulphate and a rather specific surfactant system are used to form a gelled structure by the formation of lamellar phases.
Alternatively, shear thinning gel-type detergent compositions may be formulated by adding specific ingredients to a non-gelled detergent formulation, typically at low dosage, so as to induce gellation.
Examples of this route for preparing gelled detergents are disclosed in U.S. Pat. No. 6,362,156. More specifically, this document discloses shear thinning, transparent gel-type laundry compositions comprising a polymer gum, such as Xanthan gum, which gum is capable of forming stable continuous gum networks which can suspend particles.
However, when using a polymer additive such as the polymer gum disclosed in U.S. Pat. No. 6,362,156, so as to form the gelling structure, it is generally required to carry out several specific steps in the manufacturing process in order that the gel structure is properly formed. These steps are relatively costly and make the manufacturing process rather time-consuming.
In addition, the ‘structure’ of the gel-type detergent composition disclosed by U.S. Pat. No. 6,362,156 resides in the dispersed polymeric network and not in the continuous bulk phase, which remains essentially isotropic in nature. For that reason, particles suspended in this system tend—over time—to migrate through the network leading to asymmetrical dispersions which is clearly not desirable for a gel-type detergent product.
Alternatively, U.S. Pat. No. 5,952,286 discloses skin cleansing compositions comprising lamellar phase dispersions from rad micellar surfactant systems, and additionally a structurant for establishing the lamellar phase, whereby said structurant may be a fatty alcohol. These compositions are structured as lamellar vesicles, and are opaque, and therefore unsuitable for the visual display of suspended particles or capsules.
Furthermore, copending U.S. patent application Ser. No. 10/251,738 and European patent application 02257682.1 disclose stable shear-thinning tranlucent gel laundry detergent formulations comprising a fatty acid respectively a fatty alcohol as gelling agent. Without wishing to be bound by theory, it is believed that these types of gelling agent interact with aggregates present in the respective detergent formulations so as to promote the formation of planar lamellar structures similar to those found in internally structured detergent gels, such as e.g. disclosed by WO-A-99/27065.
However, a major disadvantage of this technology relating to shear-thinning, stable, structured detergent gels is that such products structured by lamellar phases are often rather turbid in appearance. As a consequence, their transparency often leaves to be desired.
In view of this, it is an object of the present invention to find a stable shear-thinning lamellar-phase gel laundry detergent formulation which is highly transparent or translucent and provides favourable visual appearance so as to clearly demonstrate the presence of any particles, beads or capsules suspended therein. It is another object of the invention to provide a shear thinning lamellar-phase gel laundry detergent formulation that has both favourable transparency and cleaning performance.
It has been surprisingly found that these objects could be achieved by applying the shear thinning transparent gel laundry detergent composition of the present invention, containing a clarity-improving agent, as specified in claim 1.